Massive Atlantic seaweed belt is growing
Posted: Thu Oct 16, 2025 7:56 am
The Great Atlantic Sargassum Belt (GASB) is growing in extent and frequency compared with pre-2010 levels, fluctuating in size from year to year but trending upward.
The GASB is a massive chain of floating seaweed that stretches across the tropical Atlantic—from West Africa to the Caribbean and Gulf of Mexico.
It first appeared as a persistent, large-scale feature in 2011 and has recurred annually ever since.
Before 2011, sargassum was confined mostly to the Sargasso Sea.
Since 2011, satellite imagery has shown record-high biomass levels nearly every few years, notably in 2018, 2022 and 2024.
Peak totals have reached over 30–35 million metric tonnes, roughly double the early 2010s average.
The belt now stretches over 8000 km, covering more of the Caribbean, Gulf of Mexico and West African coast than ever before.
It appears earlier in the year and lasts longer into the season.
Samples show increasing nitrogen and phosphorus levels in the seaweed tissue—evidence of nutrient enrichment from sources like Amazon River runoff, fertilizer, and sewage.
Nutrient enrichment from rivers and coastal runoff, ocean warming and circulation changes favor its growth and dispersal.
Upwelling patterns and Saharan dust deliver trace nutrients like iron.
It is yet another of the marine blooms that are growing in size and intensity as the climate warms.
The GASB is a massive chain of floating seaweed that stretches across the tropical Atlantic—from West Africa to the Caribbean and Gulf of Mexico.
It first appeared as a persistent, large-scale feature in 2011 and has recurred annually ever since.
Before 2011, sargassum was confined mostly to the Sargasso Sea.
Since 2011, satellite imagery has shown record-high biomass levels nearly every few years, notably in 2018, 2022 and 2024.
Peak totals have reached over 30–35 million metric tonnes, roughly double the early 2010s average.
The belt now stretches over 8000 km, covering more of the Caribbean, Gulf of Mexico and West African coast than ever before.
It appears earlier in the year and lasts longer into the season.
Samples show increasing nitrogen and phosphorus levels in the seaweed tissue—evidence of nutrient enrichment from sources like Amazon River runoff, fertilizer, and sewage.
Nutrient enrichment from rivers and coastal runoff, ocean warming and circulation changes favor its growth and dispersal.
Upwelling patterns and Saharan dust deliver trace nutrients like iron.
It is yet another of the marine blooms that are growing in size and intensity as the climate warms.